1. Field of the Invention
This invention is directed to methods, systems, and processes for the manufacturing of fertilizer and the fertilizer product manufactured by these methods. In particular, the invention is also directed to the manufacture of fertilizers with predetermined concentrations or absences of nitrogen, phosphate and/or potassium.
2. Description of the Background
Sludge today is estimated to be produced at a rate of over 8 million dry metric tons annually or roughly about 64 dry pounds of biosolids for every individual in the United States. The term sludge has been replaced with the term biosolid which includes all forms of municipal wastes such as, for example, domestic septage, farm and factory organic wastes that are collected or otherwise find their way to waste-water treatment, sewer run offs, pharmaceutical wastes including fermentation and processing wastes, microbial digests, food wastes and food byproducts, animal manures, digested animal manures, organic sludge, organisms and microorganisms and all combinations thereof. Most all industrial wastes find their way into municipal sludge or are otherwise disposed of in landfills or as may be common in the particular industry. As can be envisioned, all forms of discarded material can and typically do wind up in municipal sludge including biologically-active molecules such as pharmaceuticals as well as their metabolized products, paper, plastics, metals and most all forms of garbage.
Biosolids are collected typically by municipalities through existing infrastructures such as sewers and other types of residential and industrial plumbing systems. Collected material is sent to one or more central facilities referred to as waste-water treatment plants. At these plants water is separated from the solids and sent through purification procedures for reclamation. The solids are either burned or transported by truck for burial or by barge for dumping into the ocean. Burning or incineration has become more common in part because of the awareness the dangers of unprocessed biosolids. In all biosolids are assumed to be not only harmful chemicals but also bioactive compounds, and pathogens. Federal, state and local regulations exist that strictly control the handling of biosolids for the safety of both workers and the public. But whether burned or buried, such procedures are highly inefficient and extremely costly.
Burning destroys most of the harmful materials present in the biosolids, but the cost in damage to the environment is always tremendous. Incinerators have been built specifically to deal with municipal waste. These incinerators create huge amounts of contaminated smoke spoiling the air within hundreds of square miles around the facility. The smoke that's emitted contains whatever contaminants as were present in the biosolids such as metals and other non-combustible components. Those contaminants settle onto fields and bodies of water creating ecological nightmares around the plants and sometimes for great distances down-wind of the plants. Although burning can produce energy, energy production is highly inefficient requiring huge amounts of biosolids to become cost effective. The amount of energy produced is always small in comparison to the amount of material incinerated. Even after burning, enormous amounts of soot remain that must be removed and disposed. As compared to the original biosolid, the soot is devoid of any positive impact to the environment whatsoever and is simply and unceremoniously buried or dumper into the ocean. Overall burning negatively increases the impact of biosolid disposal to the environment and for many years into the future.
Biosolids that have been treated to some degree of processing are classified according to federal standards established by the United States Environmental Protection Agency as Class A or Class B. “Class A” biosolids are considered free of detectable pathogens and sufficiently safe as a fertilizer for animal or human crop usage. Pathogens such as, for example, Salmonella sp. bacteria, fecal coliform indicator bacteria, enteric viruses, and viable helminth ova are below detectable levels. When pathogens can be detected in the biosolids, the USEPA has classed such treated biosolids as “Class B” implying that they are of a lower standard than the “Class A” treated biosolids. Because Class B biosolids contain pathogen indicators—and therefore potential pathogens, they are restricted in the manner by which they can be applied to animal and human crops.
The Part 503 rule (Title 40 of the Code of Federal Regulations, Part 503, incorporated herein by reference) lists six alternatives for treating biosolids so they can be classified in Class A with respect to pathogens. Alternative 1 requires biosolids to be subjected to one of four time-temperature regimes. Alternative 2 requires that biosolids processing meets pH, temperature and air-drying requirements. Alternative 3 requires that when biosolids are treated in other processes, it must be demonstrated that the process can reduce enteric viruses and viable helminthes ova, and operating conditions used in the demonstration after pathogen reduction demonstration is completed must be maintained. Alternative 4 requires that when treated in unknown processes, biosolids be tested for pathogens at the time the biosolids are used or disposed or, in certain situations, prepared for use or disposal. Alternative 5 requires that biosolids be treated in one of the Processes to Further Reduce Pathogens. Alternative 6 requires that biosolids be treated in a process equivalent to one of the Processes to Further Reduce Pathogens, as determined by the permitting authority.
Class A pathogen biosolids must also possess a density of fecal coliform of less than 1,000 most probable numbers (MPN) per gram total solids (dry-weight basis) or a density of Salmonella sp. bacteria of less than 3 MPN per 4 grams of total solids (dry-weight basis). Either of these two requirements must be met at one of the following times: when the biosolids are used or disposed; when the biosolids are prepared for sale or give-away in a bag or other container for land application; or when the biosolids or derived materials are prepared to meet the requirements for Exceptional Quality biosolids.
All biosolids applied to the land must meet the ceiling concentration for pollutants, comprising ten heavy metal pollutants: arsenic, cadmium, chromium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc. If a limit for any one of these is exceeded, the biosolids cannot be applied to the land without the incorporation of significant restrictions. Exceptional Quality (EQ) is a term used by the USEPA Guide Part 503 Rule 7 to characterize biosolids that meet low-pollutant and Class A pathogen reduction (virtual absence of pathogens) limits and that have a reduced level of degradable compounds that attract vectors.
Biosolids that are merely dried have several disadvantages for agricultural use. Biosolids have a low fertilization value, typically having nitrogen content of only about two to five percent. Volume is large and costs per unit of nitrogen are high. The heat-dried biosolids often have a disagreeable odor, particularly when moist. Also, dried pellets have low density and hardness and when blended with other commercial fertilizer materials, the pellets may segregate, and disintegrate and may not spread on the field uniformly with other more dense ingredients. The disagreeable odor associated with the use of biosolids, unless adequately treated, will continue to be present during further processing of a nitrogen rich fertilizer product, and can continue to be present in the final product. This complicates the placement of suitable fertilizer processing plants to locations that are not in close proximity to residential communities. Additionally, the longer distance that biosolids must be transported adds to the cost and logistics of disposing of this waste product. Another disadvantage to current biosolids-enhanced fertilizers is that bacterial action may continue when the material becomes moist, and under storage conditions, the material's temperature may rise to the point of auto-ignition. Hence, except for special markets that value its organic content for soil amendment or filler in blended fertilizer, there is relatively poor demand for the heat-dried biosolids product. In many cases municipalities must pay freight charges, or may offer other incentives for commercial growers to use the material. However, this is frequently still more economical than alternative disposal schemes.
The market value for agricultural fertilizers is principally based on their nitrogen content. A need exists for a practical, safe and economic method for increasing the nitrogen content of biosolids to a level approaching that of commercial mineral fertilizers, e.g., eight to twenty two percent. If such a biosolids fertilizer could be manufactured then the overall value of the biosolids product and demand for the product would likely increase. Moreover, a properly manufactured biosolids fertilizer will have an advantage in that much of its nitrogen will be of the slow release type. Slow-release or controlled release fertilizer is one in which the nutrient, e.g., nitrogen as in ammonium ions, phosphate and/or sulfate, becomes available in the soil column at rates slower than fast-available nutrients as from traditional fertilizers such as urea, ammonium sulfate and diammonium phosphate. This slower action and/or prolonged availability of the nutrient in the soil column is very desirable and provides nutrients to the plant throughout the plant growing cycle with the implication that less nitrogen needs to be applied to the soil or crop thereby reducing the potential of environmental contamination and reducing the cost of fertilizer usage. Traditional inorganic manufactured slow release nitrogen fertilizers have a price many times that of ordinary mineral nitrogen fertilizers. Under the scenario of high nitrogen biosolids-containing fertilizer production from their biosolids, municipalities would enjoy public and regulatory support for their biosolids disposition program. Such a program would ensure the regular removal of their dewatered or dried biosolids, for example, by recycling biosolids into a high nitrogen fertilizer which then can be sold directly into the mature national fertilizer distribution industry, thereby eliminating one of the major problems traditionally associated with biosolids treatment programs.
Prior attempts have been made to reach some of these objectives. U.S. Pat. Nos. 3,942,970, 3,655,395, 3,939,280, 4,304,588, and 4,519,831 describe processes for converting sewage biosolids to fertilizer. In each of these processes a urea/formaldehyde condensation product is formed in situ with the biosolids. Thus, the processes require the handling of formaldehyde, a highly toxic lachrymator and suspected cancer-causing agent.
Other processes require costly process equipment and/or special conditions not readily incorporated in existing sewage treatment facilities (see, Japanese Patent No. 58032638; French Patent No. 2,757,504).
A simple method for increasing the nitrogen in biosolids would be to blend commercial nitrogen fertilizer materials to the wet biosolids prior to drying and pelletizing. There are only a few high-nitrogen fertilizer materials that are economical for use in agriculture. Examples include: ammonia (82 wt. percent N), urea (46 wt. percent N), and ammonium nitrate (33.54 wt. percent N). Ammonia has high volatility and is subject to strict regulation of discharges to the atmosphere. Urea is a solid that adsorbs moisture quite readily and makes the sludge more difficult to dry. Urea is also highly susceptible to breakdown to ammonia by the microbes and enzymes in biosolids if they are not properly prepared, resulting in nitrogen loss and an odor problem. Ammonium nitrate is a strong oxidizer and can result in a potential explosion problem which has all but eliminated this fertilizer from the commercial market after 2000. All of these fertilizers have high nitrogen content, but are less than ideal for combining with biosolids absent special processing.
Other references, such as European Patent No. 0143392, Japanese Patent No. 9110570 A2, and “Granulation of Compost From Sewage Sludge. V. Reduction of Ammonia Emission From Drying Process”, Hokkaidoritsu Kogyo Shikenjo Hokoku, 287, 85-89 (1988) fail to disclose the use of acids with ammonium sulfate additions and do not discuss the issue of corrosion of steel process equipment under acid conditions.
Over the past thirty years alkaline stabilization of biosolids has been a standard and successful method of making biosolids into beneficially useful materials that can be used principally as soil-conditioning materials. Because these alkaline stabilized biosolids products have high calcium carbonate equivalencies, they have been produced and marketed as Agricultural liming or Ag-lime materials, usually as a replacement for calcium carbonate in farm soil management strategies. Because of this usage, the value of these materials has been restricted to only a few dollars per ton of product. However, transportation costs are high in large part due to the significant water content of the material. Amounts of water up to fifty percent render transportation economically and geographically restricted to areas close to the source of their treatment.
Thus, there is a long standing need for practical means of increasing the economic value of sewage biosolids through increasing its nitrogen content, and increasing the ability to be spread as well as a need to treat these materials such that they are converted into commodity fertilizers with physical and chemical and nutrient properties such that they can command significant value in the national and international commodity fertilizer marketplace. A series of U.S. patents, U.S. Pat. Nos. 5,984,992; 6,159,263; 6,758,879 and 7,128,880 describe methods of production of high nitrogen organically enhanced ammonium sulfate fertilizers made with biosolids utilizing a pipe-cross reactor as originated by the Tennessee Valley Authority. The pipe, tee and pipe-cross reactor are defined by the IFDC in the Fertilizer Manual (1998), p 440 as: “the pipe reactor consists basically of a length of corrosion-resistant pipe (about 5-15 m long) to which phosphoric acid, ammonia and often water are simultaneously added to one end through a piping configuration resembling a tee, thus the name ‘tee reactor.’” The tee reactor was modified by TVA to also accept an additional flow of sulfuric acid through another pipe inlet located opposite the phosphoric acid inlet, giving the unit a “cross” configuration and thus the name “pipe-cross reactor”.
Both the IFDC Fertilizer Manual (1998) and the Fertilizer Technical Data Book (2000) refer to the pipe-cross reactors. Pipe-cross reactors deliver a concentrated mix to the granulator shaping device and more efficiently evaporate undesired water from the fertilizer mix than other devices, but these references demonstrate a long-felt need for improvement, indicating that one of the shortcomings of the pipe-cross reactor is scale formation inside the pipe which can result in clogging.
The methodologies taught by this group of patents (U.S. Pat. Nos. 5,984,992; 6,159,263; 6,758,879 and 7,128,880) are plagued by problems related to the pluggage of these narrow (relative to their length) “pipe-cross” reactor configurations, the very short duration of reaction time in such “pipe-cross” reactors and the difficulty of control of the reaction temperature and pressure and retention time of the mix within such pipe-cross reactors. These pipe-cross reactors are narrow in contrast to their length, e.g., up to six to eight inches in diameter and often fifteen feet in length or longer. The plant practicing the manufacture of organically-enhanced ammonium sulfate fertilizers often had to shut down and disassemble the pipe-cross reactor either due to blockage from biosolids buildup or from destructive over heating in such reactors such that the commonly used Teflon® coating on the interior-reaction side of the reactor was melted and ruined. Further, the use of the pipe-cross reactor has the distinct disadvantage of having very short reactor retention times (usually less than twenty seconds) which is an advantage in the manufacture of traditional fertilizers like ammonium sulfate but is a disadvantage when coupled to the simultaneous processing of biosolids. Such short processing time increases the probability of untreated or non-homogenous mixing as the three material inputs pass through this reactor. Also limiting is the lack of control over the atmospheric pressure within such pipe-cross reactors since these reactors have open-ended discharges usually directly into a granulator. Related to but distinct from the lack of control of internal pressures, pipe-cross reactors also have little to no temperature control over the mix passing through the reactor.
U.S. Pat. No. 4,743,287 to Robinson describes a method to use two reaction vessels in sequence to incorporate organic biosolids into nitrogen fertilizers of low or medium nitrogen concentration (a range of four weight-percent nitrogen to a maximum of nitrogen concentration of ten weight-percent). Robinson uses his first reaction vessel to achieve very low pH values of the mixture (pH 0.2 to 1.5) to achieve hydrolysis of molecules present and to prepare the mix for reaction in a second reaction vessel. Robinson does indicate that a single reactor can be used, but only in a batch configuration and not in a continuous flow manufacturing method. Robinson also indicates that the acid and ammonia may not be injected in any order, but must be injected in sequence. This patent describes the reaction vessels capable of achieving high pressures (30 psig) with relatively long retention times as compared to the pipe-cross reactors. However, Robinson fails to meet the need for a novel and practical continuous flow method of manufacturing high nitrogen (greater than 8 wt. percent nitrogen) and biosolids-containing fertilizer products under the advantages of defined temperatures, pressures and reaction retention times. Thus, an urgent need exists for an effective, efficient, and economical process for treating biosolids.